Diversity receiving system



Dec. 12, 1944.

M. G. CROSBY DIVERSITY RECEIVING SYSTEM Filed March 13, 1942 2Sheets-Sheet l ATTORNEY Dec. l2, 1944.

M. G. CROSBY DIVERSITY RECEIVING SYSTEM Filed March l5, 1942 2-Sheets-Sheet 2 Patented Dec. 12, 1944 DIVERSITY RECEIVING SYSTEM MurrayG. Crosby, Riverhead, N. Y., assigner to Radio Corporation of America, acorporationl of Delaware Application March 13, 1942, Serial No; 434,508,

(Cl. Z50- 20) 17 Claims.

This invention relates to a signal receiving system employing aplurality of spaced antennas for reducing the effects of fading. Such areceiving system is known as a diversity system.

In such diversity receiving systems, the phases of the received energiesat the different antennas do not remain constant but vary relative toone another With fading. The problem of overcoming the variability ofthe phase relations between the voltages from the different receivingantennas by automatically maintaining a predetermined phase relation, sothat the radio frequency or intermediate frequency voltages may becombined before rectification, has been dealt with in my United StatesPatent 2,042,831, granted June 2,A 1936. In my copending application ledDecember 31, 1941, Serial No. 425,021, I have disclosed a diversityreceiving system in which, among other things, the receivers function tocontrol the phase of one of the incoming signal voltages obtained from areceiver byvarying a phase shifter or a reversing system. It is alsoknown that in a diversity receiving system, the rectified energy fromthe various receivers may be combined and utilized to control the gainof the receivers. Such an arrangement is described, for example, in myUnited States Patent 1,835,761, granted December 8, 1931.

The present invention provides improvements in diversity receivingsystems and has for one of its objects to prevent distortion in theiinal utilization circuit due to carrier cancellation when the carriersreceived on two or more antennas are in opposed phase and ofsubstantially equal magnitude.

In accordance with one embodiment of the invention, the carriers arecombined in Iaiding phase relation and also in opposing phase relation,and only those components which are in aiding phase relation made tocontribute the major portion ofthe output for subsequent utilization.

Other objects and features of the invention will appear hereinafter froma reading of the followf ing description, which is accompanied bydrawings wherein Figs. 1, 2 and 3 illustrate three different embodimentsof the present invention as applied to diversity receivers.

In the drawings, the same parts have been labeled by the same referencecharacters throughout the figures.

Referring to Fig. 1 in more detail, there is shown my preferred form ofdiversity receiving system for receiving amplitude modulated waves. Thissystem includes a pair of geographically level at the inputs of thedevices'.

spaced antennae A and A', respectively feeding identical heterodynereceivers I, 2, 3 and I', 2 and 3. The high frequency oscillator Ofurnishes beating energy to the detectors 2 and 2' of the two receiversso that the intermediate frequencies obtained in band pass intermediatefrequency amplifiers 3 and 3 are the same. Boxes I and I', which couplethe antennas to the detectors, represent radio frequency amplifiers.rIfhe output of intermediate frequency amplifier 3 is fed to the primaryWinding of transformer 4 Whose secondary winding feeds opposed voltagestothe anodes of diode rectiers 6 and'l, while the output of intermediatefrequency amplier 3, is fed to primary winding of transformer 5whose'secondary winding is connected to the mid point of the secondarywinding of transformer 4, to thereby feed cophasal voltages to theanodes of tubes 6 and l. Transformers 4 and 5 are band pass tunedtransformers which are tuned to pass the signal frequency rangeconsisting of the carrier and side bands. Each winding of bothtransformers is tuned by means of a variable condenser, as shown. Acommon diode resistor I6 is placed between the cathodes of the diodesand one terminal of the secondary winding of transformer 5. This commondiode resistor is shunted by a by-pass condenser 22 which provides apath of low impedance to energy of the operating frequency. The cathodesof the diodes are grounded by means of connection I'I.

Rectied output from the diodes 6 and 'I is obtained by means of lead I8which couples the high potential side of diode resistor I6 to the gridof audio frequency amplifier I0. Also connected to lead I8 is a timeconstant circuit RC which provides an automatic volume control for tworeceivers by way of AVC leads 2) and 2l. Lead 20 is connected to thegrids of apparatus I and 3 in one receiver, while lead 2l is connectedto the grids of apparatus I and 3' in the other receiver, in order tovary the grid bias of these ampliers in accordance with variations insignal strength, so as to maintain a constant signal Time constantcircuit RC has such values to assure that the automatic volume controlwill only remove slow variations of signal intensity incontradistinction to the fast variations of the modulation. The outputof audio frequency amplier IIJ feeds into an audio frequency transformerI4, in turn coupled to a jack l5 for utilization by 'a headphone,loudspeaker, or other suitable apparatus -(not shown). As an example,the apparatus which may be plugged into jack I5 may be a broadcastingsystem for rebroadcasting the signals received on the diversity system.

In the operation of Fig. 1, the signals received on antenna A areapplied to transformer 4 which supplies them in opposing phase relationto the anodes of detectors 6 and 'I. The signals received on antenna A',on the other hand, are applied to transformer 5 which applies them tothe anodes of detectors 6 and 1 cophasally. Assuming that the signalsreceived over the two antennas are at 180 phase relation, it will beevident that one of the diodespfor example diode 6, will receive a higheffective carrier which is in effect the-summation of the two carriers,while the other diode 'I will receive a low effective carrier which isthe difference of the two received carriers. If, as an illustration, thesignal from receive'r I, 2, 3 produces in each half of the secondarywinding of transformer 4 a volta-ge of 1.2 volts, and signals receivedin receiver I', 2', 3 produce in the secondary winding of transformer 5a voltage of .one volt, there will be applied to detector 6 a resultantvoltage of 2.2 volts while there will be appliedto detector 'I' aresultant voltage of .2 volt. The resultant voltage of 2.2 volts appliedto detector 6 will appear as a rectified voltage of 2.2 volts acrossdiode resistor I5, which value is available in lead I8 for utilizationby audio frequency amplier I 0, and also available for automatic volumecontrol purposes. Because the resistor I6 is common to both diodes 6 and1, the voltage appearing across this resistor serves to bias diode I sothat its anode is negative by an amount which in this example isapproximately 2.2 volts. Since the resultant intermediate frequencyvoltage applied to detector 'I is the resultant of the opposing carriersand is only .2 volt, the rectified voltage across common diode resistorI6 of a value of 2.2 volts will so bias detector I that it cannot drawcurrent. It can be seen that with an opposite phase relation of zerodegrees, the diode 6 will be biased bythe direct current from diode 1,so that the diode 6 will not draw current.

The present invention thus provides an arrangement whereby only onediode detector or the other passes current when the phase relationsbetween the carriers are either at zero or 180. This detector whichpasses current is the one which receives the carriers in aiding phaserelation, When the carriers impressed on transformers 4 and 5 from thereceivers are at 90 phase relation, however, both diodes will drawcurrent by virtue of the fact that at this particular phase relation thecarriers do not buck or aid,

and balanced resultant radio frequency voltages are fed to the anodes ofthe two detectors 6 and '1. This balancing condition for a 90 phaserelation exists irrespective of the relative intensity or magnitude ofthe radio frequency carriers impressed on transformers 4 and 5. Forintermediate values of phase relation between zero and 90 and between 90and 180, one diode will draw more current than the other, and the diodewhich passes the greater current will bias the diode passing the weakercurrent, so that the weaker current-passing diode does not contribute asmuch rectified output as the other.

Fig. 2 illustrates another form of the diversity receiving system inaccordance with the invention in which there arel employed separatediode resistors 8 and 9 for the respective diode rectiiiers 6 and 1.Diode 6 has audio amplifier I2 coupled across the resistor 8, whilediode I has an audio amplifier I3 coupledl across its resistor 9, theoutputs or anodes of both amplifiers I2 and I3 being connected inparallel by means of connection 23. The combined amplified outputs oftubes I2 and I3 pass through audio transformer I4 for utilization injack I5 in the manner described above in connection with Fig. 1. Becauseof the use of separate diode resistors 8 and 9, both diodes will alwayspass current at all phase relations of the incoming carriers, althoughat a phase relation of zero or 180 between the two.carriers, thatdetector which is receiving the opposed carriers will produce aninappreciable part of the output.

For example, assuming that diode 6 is receiving a resultant radiofrequency Voltage which, in effect, is the summation of the twocarriers, while diode 'Lis receiving a, resultant radio frequencyvoltage which is the difference of the two carriers, then there will bea large current flow through resistor 8 and a small current flow throughresistor 9. 'I'lie voltage across resistor 8 will be available foramplification by amplifier I2 and will produce the predominant output intransformer VI4, While the voltage across resistor 9 (which in thecondition assumed above is much smaller than that across resistor 8)will be amplifled by tube I3 to produce an inappreciable part of theoutput available in transformer I4, Putting it in other words, theeffectiveness of the combining system of Fig. 2 is dependent upon thefact that that detector receiving the energy from the two antennascombined out of phase has a low value of carrier and consequently a lowaudio output, whereas that detector receiving the carriers in phase hasa high effective carrier and therefore a high output. When the carrierswhich are applied to transformers 4 and 5 are 90 out of phase, bothdetectors 6 and 'I will contribute the same amount of energy to theamplifiers I2 and I3, irrespective of the relative magnitudes of thecarriers. But, since there is no distortion between the carriers forthis particular phase relationship of as is the case for a zero or phaserelation condition, there is no necessity t0 have the output of onediode or the other predominate. .The overall effect of the system ofFig. 2 is that when the carriers oppose or aid, the diode rectifierwhich is fed with the opposing carriers does not contribute enoughoutput to allow distortion to become objectionable.

Fig. 3 is a modification of Fig. 2 and differs therefrom primarily inthe method of combining the outputs of the two diodes G and 7. In 3, thecathode of diode 6 is connected through resistors 8 and 9 to the anodeof diode I in a series arrangement. Thus, in effect, the connections ofthe anode and cathode electrodes of diode 1 to the secondary oftransformer 4 and the resistor 9 are reversed with respect to theconnections of the same diode to the same elements in Fig. 2. With thearrangement of Fig. 3, the currents through the resistors 8 and 9 arealways in the same direction, and therefore it is possible to employ asingle audio amplifier tube I6 whose input electrodes are connectedacross the two resistors 8 and 9. The arrows indicate the directions ofthe rectified current through resistors 8 and 9. It will be noted thatthe directions o-f current ilow are the same so that this seriesconnection applies the aiding combination of detected voltages to thegrid of amplifier I6. Except for the foregoing difference, the operationof Fig. 3 is the same as that of Fig. 2.

What is claimed is:

1. The method of operating a diversity radio receiving system having apair of antennas feeding energy to a pair of rectiers which comprisesfeeding signal energy from one antenna in opposed relation to certainelectrodes of said pair of rectiers, feeding signal energy from theother antenna and of the same frequency as said yfirst signal energy tothe same electrodes of said pair of rectifiers in cophasal relation,deriving rectified energy from both of said rectifiers in a commonutilization circuit, causing one of said rectifiers to produce thepredominantly useful alternating current output when the two carriersreceived by said antennas areat 180 phase relationy and causing theother of said rectifiers to produce the predominantly useful alternatingcurrent output when the two carriers received by said antenna are atZero degrees phase relation.

2. The method of operating a diversity radio receiving Vsystem having apair of antennas feeding energy to a pair of rectifiers which comprisesfeeding signal energy from one antenna in opposed relation to certainelectrodes of said pair of rectifiers, feeding signal energy from theother antenna and of the same frequency as said first signal energy tothe same electrodes of said pair of rectiers in cophasal relation,deriving rectied energy from both of said rectifiers in a commonutilization circuit, causing both rectifiers to contribute equal valuesof useful output current when the two carriers received by said antennasare at a 90 phase relation, and causing one of said rectiers to producethe predominantly useful output current when the two carriers receivedby said antennas depart from a 90 phase rela-` tion.

3. The method of operating a diversity radio receiving system having apair of antennas feeding energy to a pair of rectiers which comprisesfeeding signal energy from one antenna in opposed relation to certainelectrodes of said pair of rectifiers, feeding signal energy from theother antenna and of the same frequency as said first signal energy tothe same electrodes of said pair of rectii'iers in cophasal relation,deriving rectified energy from both of said rectifiers in a commonutilization circuit, causing both i'ectiers to contribute equal valuesof useful output current when the two carriers received by said antennasare at a 90 phase relation, causing only one of said rectifiers toproduce useful output current when the two carriers received by saidantennas are at 180 phase relation, and causing only the other of saidrectifiers to produce useful output current when the two carriersreceived by said antennas are at zero phase relation.

4. The method of operating a diversity radio receiving system having apair of antennas feed- .ing energy to a pair of rectifiers whosecorresponding electrodes are connected together, which comprises feedingsignal energy from one antenna in opposed relation to like electrodes ofsaid pair of rectifiers, feeding signal energy from the other antennaand of the same frequency as the first signal energy-to the samelikenelectrodes of said pair of rectifiers in cophasalrelation, derivingrectified ener-gy from both of. said rectifiers in a common utilizationcircuit, whereby one of said rectiers receives a higher resultant highfrequency voltage than the other when the two carriers depart from a 90phase relation, and causing that rectifier receiving the higherresultant high frequency voltage to bias the other rectifier to reducethe tendency for current iiow therethrough.

5. The method of operating a diversity radio vreceiving system having apair of antennas feeding energy to a pair of rectifiers which comprisesfeeding signal energy from one antenna in opposed relation t0 certainelectrodes of said pair of rectifiers, feeding signal ener-gy from theother antenna and of the same frequency as said first signal energy tothe same electrodes of said pair of rectiflers in cophasal relation,deriving rectified energy from both of said rectifiers in a commonutilization circuit, whereby one of said rectifiers receives a higherresultant high frequency voltage than the other when the two carriersdepart from a 90 phase relation, and utilizing the rectified combinedenergies to bias negatively that rectifier which receives the lowerresultant high frequency voltage.

6. In a radio receiving system, a pair of antennae feeding separatereceivers, a pair of detectors having their corresponding electrodesconnected together, means for feeding energy from one receiver to theanodes of said detectors in opposed phase relation, means for feedingenergy from the other receiver to the anodes of said detectors incophasal relation, a common bias resistor through which flows thedetected currents from' both detectors, and means for utilizing thevoltage drop across Said resistor.

7. In a radio receiving system, a pair of antennae feeding separatereceivers, each receiver having an amplifier, a mixer circuit forproducing an intermediate frequency output, and an intermediatefrequency amplier; a pair of rectifier circuits each including adischarge device having anode and cathode electrodes, a pair of likeresistors connected in series between the cathodes of said devices, atransformer having a primary `winding coupled to the intermediatefrequency amplifier of one receiver and a secondary winding coupled tothe anodes of said devices for ap- "plying opposed voltages thereto,another transformer having a primary winding coupled to the intermediatefrequency amplier of the other receiver and a secondary winding coupledbetween the electrical center of the rst secondary winding and thejunction point of said resistors for applying in-phase voltages to theanodes of said'devices, a condenser for each of said windings of saidtransformers for tuning the same to pass the signal frequency range ofcarrier and side bands, and a pair of audio frequency amplifiers one ofwhich has its input electrodes across one of said resistors while theother has its input electrodes across the other of said resistors, and aconnection between the output electrodes of said audio amplifiers forcombining the outputs thereof.

8, In a radio receiving system, a pair of antennae feeding separatereceivers, each receiver` having an amplier, a mixer circuit forproducing an intermediate frequency output, and an intermediatefrequency amplifier; a pair of rectifierv circuits each including adischarge device having anode and cathode electrodes, a band passtransformer having a primary winding coupled to the intermediatefrequency amplifier of one receiver and a secondary winding coupled tothe anodes of said devices for applying opposed voltages thereto,another band pass transformer having a primary winding coupled to theintermediate frequency amplifier of the other receiver and a secondarywinding coupled between the electrical center of the first secondarywinding and the cathodes of Said devices for applying in-phase voltagesto the anodes of said devices, and audio frequency amplifier meanshaving its input electrodes coupled to said devices.

9'. In a radio receiving system, a pair of antennae feeding separatereceivers, each receiver having an amplifier, a mixel` circuit forproducing an intermediate frequency output, and an intermediatefrequency amplifier; a pair of rectier circuits each including adischarge device having anode and cathode electrodes, a pair of likeresistors connected in series between the cathodes of said devices, aby-pass condenser across each resistor of said pair, a connection fromground to the junction point of said resistors, a transformer having aprimary winding coupled to the intermediate frequency amplifier of onereceiver and a secondary winding coupled to the anodes of said devicesfor applying opposed voltages thereto, ano-ther transformer having aprimary winding coupled to the intermediate frequency amplifier of theother receiver and a secondary winding coupled between the electricalcenter of the first secondary Winding and the junction point of saidresistors for applying in-phase voltages to the anodes of said devices,a condenser for each of said windings of said transformers for tuningthe same to pass the signal frequency range of carrier and side bands,and a pair of audio frequency amplifiers one of which has its inputelectrodes across one of said resistors While the other has its inputelectrodes across the other of said resistors, and a connection betweenthe output electrodes of said audio amplifiers for combining the outputsthereof.

anode and cathode electrodes, a resistive connection between the cathodeof one device and the anode of the other device, a band pass transformerhaving a primary winding coupled to the intermediate frequency amplifierof one receiver and a secondary winding coupled to the anode of said onedevice andthe cathode of said other device for applying opposed voltagesto said last electrodes, an-other band pass transformer having a primarywinding coupled to the intermediate frequency amplifier of the otherreceiver and a secondary winding coupled between the electrical centerof the first secondary winding and the electrical center of saidresistive connection for applying in-phase voltages to said lastelectrodes, and an audio frequency amplifier having its input electrodesconnected across said resistive connection.

' l1. In a radio receiving system, a pair of antennae feedingseparatereceivers, each receiver having an amplifier, a mixer circuit forproducing an intermediate frequency output, and an intermediatefre-quency amplifier; a pair of rectifier circuits each including adischarge device having anode and cathode electrodes, a resistiveconnection between the cathodes of said devices, a band pass transformerhaving a primary winding coupled to the intermediate frequency amplifierof one receiver and a secondary winding coupled to the anodes of saiddevices for applying opposed voltages the-reto, another band passtransformer having a primary winding coupled to the intermediatefrequency amplier of the other receiver and a secondary winding coupledbetween the electrical center of the first secondary winding and theelectrical center of said resistive connection for applying iii-phasevoltages to the anodes of said devices, a by-pass condenser acrossv eachhalf of said resistive connection, and audio frequency translation meanscoupled to said rectifier circuits for utilizing the currents rectifiedthereby.

12. The method of combining signals having the same intelligence andwhich are varying in relative phase and amplitude, which comprisesproducing a first combination of the energies -of a pair of said signalshaving the same frequency, producing a second combination of said sameenergies with a phase of combination opposite to that of said firstcombination, and causing the stronger of said two combinations tocontribute a major portion of the output for utilization.

13. In a radio receiving system, a pair of energy collectors feedingseparate receivers, a pair of detectors having their correspondingelectrodes connected together, means for feeding energy from onereceiver to like electrodes of said detectors in opposed phase relation,means for feeding energy from the other receiver to the same likeelectrodes of said detectors in cophasal rela'- tion, a common biasresistor through which fiows the detected currents from both detectors,and means for utilizing the voltage drop across said resistor.

14. In a radio receiving system, a pair of energy collectors feedingseparate receivers, a pair of detectors having their correspondingelectrodes connected together, a circuit for feeding signal 'energy fromone receiver to like electrodes of said detectors in opposed phase, acircuit for feeding signal energy of the same frequency as said rstsignal energy t0 the same like electrodes in cophasal relation, a commonbias resistor through which fiows the detected currents from bothreceivers, and an audio frequency utilization circuit coupled to saidresistor for utilizing the voltage drop across the resistor.

15. In a radio receiving system, a pair of energy collectors feedingseparate receivers, a pair of detectors having their correspondingelectrodes connected together, a circuit for feeding signal energy fromone receiver and of a frequency lower than that impressed upon said onereceiver to the anodes of vsaid detectors in opposed phase relation, acircuit for feeding signal energy from the other receiver and of thesame lower frequency mentioned above to the anodes of` said detectors incophasal relation, a common bias resistor through which flows thedetected currents from both receivers connected between the cathodes andthe anodes of said detectors, and an electron discharge devicetranslation circuit coupled to said resistor for utilizing the voltagedrop thereacross.

16. In a radio receiving system, a pair of energy collectors feedingseparate receivers, each receiver having means for producing anintermediate frequency output, a pair of rectifier circuits eachincluding a discharge device having anode and cathode electrodes, a bandpass transformer having a primary Winding coupled to the intermediatefrequency output of one receiver and a secondary winding coupled to theanodes of said devices for applying opposed voltages thereto, anotherband pass transformer having a primary winding coupled to theintermediate frequency output of the other. receiver and a secondarywinding coupled between the electrical center vof the first secondarywinding and the cathodes of said devices for applying in-phase voltagesto the anodes of said devices, and audio frequency utilization meanscoupled to said devices.

17. In a radio receiving syste-m, a pair of energy collectors feedingseparate receivers, each receiver having means for producing anintermediate frequency output, a pair of rectier circuits each includinga discharge device having anode and cathode electrodes, a resistiveconnection between the cathode of one device and the anode of the otherdevice, a band pass Jtransformer having a primary Winding coupled to theintermediate frequency output of one receiver and a secondary windingcoupled to the anode of said one device and the cathode of said otherdevice ior applying opposed voltages to said last elec- ';rodes, anotherband pass transformer having a primary winding coupled to theintermediate irequency output of the other receiver and a secondaryWinding coupled between the electrical center )f the first secondaryWinding and the electrical :enter of said resistive connection forapplying .n-phase voltages to said lastl electrodes, and an electrondischarge device translation circuit connected across said resistiveconnection.

MURRAY G. CROSBY.

